U.S. patent application number 11/808679 was filed with the patent office on 2007-12-27 for band allocation method and radio communication system.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Yoshikazu Kakura, Kengo Oketani, Akihisa Ushirokawa.
Application Number | 20070297381 11/808679 |
Document ID | / |
Family ID | 38512649 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070297381 |
Kind Code |
A1 |
Oketani; Kengo ; et
al. |
December 27, 2007 |
Band allocation method and radio communication system
Abstract
A radio communication system for covering a service area with a
plurality of cells and dividing and allocating a system band of
each cell to a mobile station has a division pattern server and a
base station. The division pattern server decides a division
pattern indicating a pattern of dividing the system band which is
commonly applied to a predetermined range to which the plurality of
cells belong. The base station divides the system band into two or
more bands, using the division pattern decided by the division
pattern server, and allocates the band as a pilot transmission
frequency band to the mobile station accommodated in the cell
constructed by the base station.
Inventors: |
Oketani; Kengo; (Tokyo,
JP) ; Kakura; Yoshikazu; (Tokyo, JP) ;
Ushirokawa; Akihisa; (Tokyo, JP) |
Correspondence
Address: |
MCGINN INTELLECTUAL PROPERTY LAW GROUP, PLLC
8321 OLD COURTHOUSE ROAD
SUITE 200
VIENNA
VA
22182-3817
US
|
Assignee: |
NEC CORPORATION
Tokyo
JP
|
Family ID: |
38512649 |
Appl. No.: |
11/808679 |
Filed: |
June 12, 2007 |
Current U.S.
Class: |
370/338 |
Current CPC
Class: |
H04L 5/0048 20130101;
H04W 16/04 20130101; H04L 5/0016 20130101 |
Class at
Publication: |
370/338 |
International
Class: |
H04Q 7/24 20060101
H04Q007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 19, 2006 |
JP |
2006-168722 |
Claims
1. A band allocation method for dividing and allocating a system
band of each cell to a mobile station in a radio communication
system for covering a service area with a plurality of cells,
comprising: setting the same division pattern indicating a pattern
of dividing said system band to a plurality of base stations
constructing each of the plurality of cells belonging to a
predetermined range; and dividing said system band into two or more
bands, using said set division pattern at said plurality of base
stations, and allocating said band as a pilot transmission
frequency band to the mobile station accommodated in the cell
constructed by said base station.
2. The band allocation method according to claim 1, further
comprising collecting information of the division pattern desired
by said plurality of base stations belonging to said predetermined
range, and deciding the division pattern applied to said
predetermined range based on said collected information.
3. The band allocation method according to claim 1, further
comprising determining beforehand a plurality of division pattern
candidates, and applying commonly a selected division pattern from
the candidates to said plurality of base stations belonging to said
predetermined range.
4. The band allocation method according to claim 1, wherein the
pilot signals transmitted at the same timing and at the same
frequency are pilot sequences having the same sequence length.
5. The band allocation method according to claim 1, further
comprising allocating the bands into which said system band is
divided to a plurality of mobile stations for pilot signal
transmission at said base station, and permitting any of said
plurality of mobile stations to transmit a data signal in said
band, based on the reception quality of the pilot signal from said
plurality of mobile stations to which said bands are allocated for
pilot signal transmission.
6. The band allocation method according to claim 5, further
comprising allocating the bands into which said system band is
divided to the plurality of mobile stations by frequency division
multiplexing for pilot signal transmission at said base
station.
7. The band allocation method according to claim 5, further
comprising allocating the bands into which said system band is
divided to the plurality of mobile stations by code division
multiplexing for pilot signal transmission at said base
station.
8. The band allocation method according to claim 5, further
comprising allocating the bands into which said system band is
divided to the plurality of mobile stations by a hybrid of
frequency division multiplexing and code division multiplexing for
pilot signal transmission at said base station.
9. A radio communication system band for covering a service area
with a plurality of cells and dividing and allocating a system band
of each cell to a mobile station, wherein the same division pattern
indicating a pattern of dividing said system band is set to a
plurality of base stations constructing each of the plurality of
cells belonging to a predetermined range, said system band is
divided into two or more bands, using said set division pattern at
said plurality of base stations, and said band is allocated as a
pilot transmission frequency band to the mobile station
accommodated in the cell constructed by said base station.
10. A radio communication system band for covering a service area
with a plurality of cells and dividing and allocating a system band
of each cell to a mobile station, comprising: a division pattern
server for deciding a division pattern indicating a pattern of
dividing said system band to be applied commonly to a predetermined
range to which a plurality of cells belong; a base station for
dividing said system band into two or more bands, using said
division pattern decided by said division pattern server, and
allocating said band as a pilot transmission frequency band to the
mobile station accommodated in the cell constructed by said base
station.
11. The radio communication system according to claim 10, wherein
said division pattern server collects information of the division
pattern desired by said plurality of base stations belonging to
said predetermined range, and decides the division pattern applied
to said predetermined range based on said collected
information.
12. The radio communication system according to claim 10, wherein
said division pattern server determines beforehand a plurality of
division pattern candidates, and applies commonly a selected
division pattern from the candidates to said plurality of base
stations belonging to said predetermined range.
13. The radio communication system according to claim 9, wherein
the pilot signals transmitted at the same timing and at the same
frequency are pilot sequences having the same sequence length.
14. The radio communication system according to claim 10, wherein
the pilot signals transmitted at the same timing and at the same
frequency are pilot sequences having the same sequence length.
15. The radio communication system according to claim 9, wherein
said base station allocates the bands into which said system band
is divided to a plurality of mobile stations for pilot signal
transmission, and permitting any of said plurality of mobile
stations to transmit a data signal in said band, based on the
reception quality of the pilot signal from said plurality of mobile
stations to which said bands are allocated for pilot signal
transmission.
16. The radio communication system according to claim 10, wherein
said base station allocates the bands into which said system band
is divided to a plurality of mobile stations for pilot signal
transmission, and permitting any of said plurality of mobile
stations to transmit a data signal in said band, based on the
reception quality of the pilot signal from said plurality of mobile
stations to which said bands are allocated for pilot signal
transmission.
17. The radio communication system according to claim 15, wherein
said base station allocates the bands into which said system band
is divided to the plurality of mobile stations by frequency
division multiplexing for pilot signal transmission.
18. The radio communication system according to claim 16, wherein
said base station allocates the bands into which said system band
is divided to the plurality of mobile stations by frequency
division multiplexing for pilot signal transmission.
19. The radio communication system according to claim 15, wherein
said base station allocates the bands into which said system band
is divided to the plurality of mobile stations by code division
multiplexing for pilot signal transmission.
20. The radio communication system according to claim 16, wherein
said base station allocates the bands into which said system band
is divided to the plurality of mobile stations by code division
multiplexing for pilot signal transmission.
21. The radio communication system according to claim 15, wherein
said base station allocates the bands into which said system band
is divided to the plurality of mobile stations by a hybrid of
frequency division multiplexing and code division multiplexing for
pilot signal transmission at said base station.
22. The radio communication system according to claim 16, wherein
said base station allocates the bands into which said system band
is divided to the plurality of mobile stations by a hybrid of
frequency division multiplexing and code division multiplexing for
pilot signal transmission at said base station.
Description
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2006-168772 filed on
Jun. 19, 2006, the content of which is incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a technique for dividing
and allocating a system band to users in a radio communication
system.
[0004] 2. Description of the Related Art
[0005] At present, in the 3GPP, a next generation mobile
communication system has been examined as a 3GPP-LTE (Long Term
Evolution). As a wireless access method for up-link in the 3GPP-LTE
system, a single carrier transmission method is important (refer to
3GPP TR 25.814 v1.5.0 (2006-05)). It is assumed that a system band
(1.25 to 20 MHz) is divided and allocated to a plurality of users,
and each user transmits data in the single carrier
transmission.
[0006] FIG. 1 is a diagram showing a frame format for use in a
single carrier transmission method proposed in the 3GPP-LTE system.
Referring to FIG. 1, two SBs (Short Block) and six LBs (Long Block)
are included in a sub-frame of 0.5 msec. It is assumed that SB is
used for transmission of a pilot signal, and LB is used for
transmission of a data signal.
[0007] A CP (Cyclic Prefix) for making the frequency domain
equalization on the receiving side effectively is provided between
blocks. FIG. 2 is a view for explaining the CP. As shown in FIG. 2,
data in the rear part of each block is copied and added as the CP
before the block.
[0008] Also, in the 3GPP-LTE system, it is assumed that the system
band is divided and allocated to a plurality of users. The division
pattern is not unique, but various division patterns are assumed.
The user (mobile station) transmits the pilot signal in the band
allocated in accordance with the division pattern.
[0009] For the pilot signal in the 3GPP-LTE system, a Zadoff-Chu
sequence that is one of the CAZAC (Constant Amplitude Zero
Auto-Correlation) sequence has gained attention (refer to K. Fazel
and S. Keiser, "Multi-Carrier and Spread Spectrum Systems," John
Willey and Sons, 2003). The Zadoff-Chu sequence is represented by
formula (I). In formula (I), N denotes the sequence length, n=0, 1,
. . . , N, and q is any integer. C_k .times. ( n ) = exp .function.
[ - j2 .times. .times. .pi. .times. .times. k N .times. ( n .times.
n + 1 2 + qn ) ] ( 1 ) ##EQU1##
[0010] This CAZAC sequence has a constant amplitude (Constant
Amplitude) in both the time and frequency domains, and the periodic
auto-correlation value is always zero for a time lag other than 0
(Zero Auto-Correlation).
[0011] If the amplitude is constant in the time domain, the PAPR
(Peak to Average Power Ratio) can be suppressed. If the PAPR is
suppressed, the power consumption is lowered. Since the CAZAC
sequence can suppress this PAPR, the power consumption of the
mobile station can be lowered, whereby the CAZAC sequence is
particularly suitable for the mobile communication which high
demands for lower power consumption of the mobile station.
[0012] Also, if the amplitude is constant in the frequency domain,
the propagation path is easily estimated in the frequency domain.
Therefore, the CAZAC sequence with constant amplitude in the
frequency domain is suitable for the mobile communication to
estimate the propagation path.
[0013] Also, if the auto-correlation characteristic is excellent,
the timing of received signal is easily detected. The CAZAC
sequence having the complete auto-correlation characteristic is
suitable for the mobile communication that detects the timing from
the auto-correlation characteristic.
[0014] However, the above techniques have the following
problems.
[0015] In the 3GPP-LTE system as described above, it is assumed
that the system band is divided and allocated to a plurality of
users, and a plurality of division patterns are assumed. At each
base station, an appropriate division pattern among the plurality
of division patterns is decided and applied.
[0016] There are various factors for deciding which division
pattern is appropriate. For example, there are factors such as a
tendency of the band requested by the mobile station within each
cell, a scheduling algorithm for giving a transmission permission
to the mobile station, a difference in the received signal quality
due to distance from the base station, and interference between
cells with the cross-correlation characteristic. If the division
pattern suitable for each base station is applied in consideration
of all these factors, it is thought that the communication
environment favorable for the mobile station within the cell can be
provided.
[0017] However, for the 3GPP-LTE system, no full examination as to
how the division pattern of each base station is decided is made at
the present stage. Therefore, in the current situation, it is not
necessarily said that the communication environment favorable for
the mobile station can be provided.
SUMMARY OF THE INVENTION
[0018] An object of the present invention is to provide a radio
communication system for dividing and allocating a system band to
the user, in which the system band is divided according to an
appropriate division pattern.
[0019] In order to accomplish the above object, the present
invention provides a band allocation method for dividing and
allocating a system band of each cell to a mobile station in a
radio communication system for covering a service area with a
plurality of cells. First of all, the same division pattern
indicating a pattern of dividing the system band is set to a
plurality of base stations constructing each of the plurality of
cells belonging to a predetermined range. Subsequently, the system
band is divided into two or more bands, using the set division
pattern at the plurality of base stations, and the band is
allocated as a pilot transmission frequency band to the mobile
station accommodated in the cell constructed by the base
station.
[0020] With the invention, since the same division pattern is
instructed to the base stations belonging to the predetermined
area, and each base station divides the pilot transmission
frequency band in accordance with the instructed division pattern,
the system band can be divided according to the appropriate
division pattern. As a result, the interference of the pilot signal
between cells can be reduced.
[0021] The above and other objects, features, and advantages of the
present invention will become apparent from the following
description with references to the accompanying drawings which
illustrate examples of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a diagram showing a frame format for use in a
single carrier transmission method proposed in a 3GPP-LTE
system;
[0023] FIG. 2 is a view for explaining a CP;
[0024] FIG. 3 is a block diagram showing a mobile communication
system according to a first embodiment of the invention;
[0025] FIG. 4 is a typical view showing the transmission and
reception of an up-stream signal in the mobile communication
system;
[0026] FIG. 5 is a view showing an example in which the pilot
transmission bands are matched between two cells;
[0027] FIG. 6 is a view showing an example in which the pilot
transmission bands are unmatched between two cells;
[0028] FIG. 7 is a view showing another example in which the pilot
transmission bands are unmatched between two cells;
[0029] FIG. 8 is a view showing an example in which the division
patterns of pilot transmission frequency band are unmatched between
two cells;
[0030] FIG. 9 is a view showing an example in which the division
patterns of pilot transmission frequency band are matched between
two cells;
[0031] FIG. 10 is a view showing one example of predetermined
division patterns in the first embodiment;
[0032] FIG. 11 is a view showing the generation of orthogonal code
for use in a CDM pilot multiplex method;
[0033] FIG. 12 is a view showing one example of predetermined
division patterns in a second embodiment;
[0034] FIG. 13 is a view showing one example of predetermined
division pattern in a third embodiment;
[0035] FIG. 14 is a view showing one example of predetermined
division patterns in a fourth embodiment; and
[0036] FIG. 15 is a view showing one example of predetermined
division patterns in a fifth embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] The embodiments for carrying out the present invention will
be described below in detail with reference to the drawings.
First Embodiment
[0038] FIG. 3 is a block diagram showing a mobile communication
system according to a first embodiment of the invention. Referring
to FIG. 3, the mobile communication system of the first embodiment
has a division pattern sever 10 and a plurality of base stations
11, 12. Base stations 11, 12 are connected to division pattern
server 10. Base station 11 constructs a cell 13, and base station
12 constructs cell 14. Mobile stations 15 to 17 exist within cell
13, and mobile stations 18 to 20 exist within cell 14.
[0039] In this embodiment, a service area is configured on a cell
basis, but the cell may be further divided into sectors. In this
case, the cell may be reread as the sector in the description of
this embodiment. Though division pattern server 10 exists
separately from base stations 11, 12 in this embodiment, the
function of division pattern server 10 may be incorporated into any
base station for integration.
[0040] Division pattern server 10 receives a desired division
pattern notification from plural base stations 11, 12, decides a
pilot transmission frequency band division pattern of each base
station 11, 12 and dictates a division pattern of pilot
transmission frequency band to each base station 11, 12. The
desired division pattern notification is a message for notifying
the division pattern desired by base station 11, 12 from base
station 11, 12 to division pattern server 10, including an index
indicating the desired division pattern. An up-link is given a
predetermined system band. The division pattern indicates how to
divide the system band for use. An instruction of the division
pattern includes the index indicating the division pattern and
change timing information indicating the timing of changing the
division pattern.
[0041] Division pattern server 10 uses the same division pattern
for plural base stations 11, 12 in a predetermined range and tries
to give the desired division pattern to each base station 11, 12 if
possible, in deciding the division pattern of pilot transmission
frequency for each base station 11, 12. For example, the division
pattern desired by the largest number of base stations 11, 12 among
the division patterns desired from base stations 11, 12 in the
predetermined range may be given to all base stations 11, 12 in the
predetermined range. The range for allocating the same division
pattern can be set beforehand.
[0042] Base station 11, 12 selects the division pattern suitable
for the self cell, based on a band allocation request received from
each mobile station within the self cell, and notifies it as a
desired division pattern notification to division pattern server
10. The band allocation request includes band information requested
by the mobile station (request band information).
[0043] For example, base station 11, 12 tallies up request band
information included in the band allocation requests received from
the mobile stations for a fixed period. And from the tally result,
base station 11, 12 decides the division pattern capable of
allocating the band as requested to the largest possible mobile
stations and notifies it to division pattern server 10.
[0044] Also, base station 11, 12 stores the division pattern
dictated from division pattern server 10, and divides the system
band according to its division pattern. And base station 11, 12
allocates any of the pilot transmission frequency bands divided
according to the dictated division pattern to the mobile station
that sends the band allocation request. Specifically, the division
pattern may be changed at the designated timing in accordance with
the index and change timing information included in the instruction
of the division pattern.
[0045] Mobile stations 15 to 20 transmit, as a pilot signal, the
CAZAC sequence of predetermined sequence length conforming to the
pilot transmission frequency band allocated from base station 11,
12. Thereby, the pilot signal transmitted at the same timing and at
the same frequency is the CAZAC sequence having the same sequence
length, whereby the cross-correlation is suppressed.
[0046] Next, a method for allowing division pattern server 10 to
decide the pilot transmission frequency division pattern of each
base station 11, 12 will be described below in detail.
[0047] FIG. 4 is a typical view showing the transmission and
reception of an up-stream signal in the mobile communication
system. In a cellular environment where the service area is divided
into two or more cells, as shown in FIG. 4, a received signal of
up-link in base station contains an up-stream signal from mobile
station in another cell (particularly adjacent cell), mingled with
an up-stream signal from mobile station within the self cell. In
FIG. 4, the up-stream signals from mobile station #2 in cell #2
which is constructed by base station #2 reach not only base station
#2 but also base station #1. Also, the up-stream signals from
mobile station #3 in cell #3 which is constructed by base station
#3 reach not only base station #3 but also base station #1. These
may cause interference between cells.
[0048] Accordingly, in order that base station excellently captures
the pilot signal from mobile station within the self cell at the
up-link, it is desired to sufficiently suppress the pilot signal
transmitted from mobile station in another cell. To suppress the
pilot signal from mobile station in another cell, it is preferred
to use the pilot sequence having small cross-correlation value at
each base station. In this embodiment, the up-link is noticed, but
the same thing can be said for the down-link.
[0049] As described above, in the 3GPP-LTE system, it is favorable
that the CAZAC sequence is used as the pilot sequence. In this
embodiment, the CAZAC sequence is used as the pilot sequence.
[0050] The cross-correlation characteristic of the CAZAC sequence
greatly depends on the sequence length. In the CAZAC sequence, if
the sequence length is equal, the cross-correlation characteristic
is excellent, but if the sequence length is different, it is
typically worse.
[0051] Also, in the CAZAC sequence, if the sequence length is prime
number or includes a large prime number, the cross-correlation
characteristic is very excellent. That is, the cross-correlation
value is small. Conversely, if the sequence length number is a
composite number of small prime numbers only (e.g., number to the
power of 2 or 3), the cross-correlation characteristic is greatly
worse. That is, the cross-correlation value includes a large
value.
[0052] More specifically, if the sequence length of the Zadoff-Chu
sequence (the sequence length is denoted as "N") is prime number,
the cross-correlation value of any sequence is always kept at 1/ N.
For example, if the sequence length N is equal to 127 (prime
number), the cross-correlation value is always 1/ 127. On the
contrary, if the sequence length N is equal to 128 (2.sup.7), the
worst value (maximum value) of the cross-correlation value is 1/ 2.
Also, in view of the number of sequence, if the sequence length N
is prime number, there is an abundance of (N-1) sequence where the
cross-correlation value is 1/ N.
[0053] Therefore, from the viewpoint of the cross-correlation
characteristic, it is proposed that the CAZAC sequence in which the
sequence length is prime number and equal between cells and the
parameter (q in formula (1)) is different for each cell is given as
the pilot sequence to each cell. Further, since the (N-1) sequence
with small cross-correlation can be taken by making such
allocation, the pilot sequence may be reused for every (N-1) cells
to repeat the pilot sequence for (N-1) cells.
[0054] Also, the pilot sequence length is coincident with the
number of sub-carriers allocated to each mobile station, and the
number of allocated sub-carriers is proportional to the allocated
frequency bandwidth. That is, the pilot sequence length is
proportional to the allocated frequency bandwidth. Accordingly, to
reduce the cross-correlation between pilot sequence, it is required
that the pilot sequence length (frequency bandwidth) is made equal
between cells to fully match the pilot transmission bands.
[0055] FIG. 5 is a view showing an example in which the pilot
transmission bands are matched between two cells. Referring to FIG.
5, the pilot transmission bandwidth of cell #1 and the pilot
transmission bandwidth of cell #2 are both 5 MHz, and their pilot
transmission bands are fully matched on the frequency axis. In this
case, the cross-correlation between cell #1 and cell #2 is
smaller.
[0056] FIG. 6 is a view showing an example in which the pilot
transmission bands are unmatched between two cells. Referring to
FIG. 6, the pilot transmission bandwidth of cell #1 is 5 MHz while
the pilot transmission bandwidth of cell #2 is 2.5 MHz. Therefore,
their pilot transmission bands are not fully matched on the
frequency axis. In this case, the cross-correlation between cell #1
and cell #2 is larger.
[0057] FIG. 7 is a view showing another example in which the pilot
transmission bands are unmatched between two cells. Referring to
FIG. 7, the pilot transmission bandwidth of cell #1 and the pilot
transmission bandwidth of cell #2 are both 5 MHz, but their pilot
transmission bands are not fully matched on the frequency axis. In
this case, the cross-correlation between cell #1 and cell #2 is
larger.
[0058] In the 3GPP-LTE, the system band (1.25 to 20 MHz) is divided
into plural sub-bands. And each of the divided frequency bands
becomes the pilot transmission frequency band of mobile station. If
the division patterns are different between cells, the pilot
transmission bands may be different on the frequency axis. Then,
the cross-correlation is larger, so that the interference between
cells is increased.
[0059] FIG. 8 is a view showing an example in which the division
patterns of pilot transmission frequency band are unmatched between
two cells.
[0060] Referring to FIG. 8, the system band of 10 MHz is divided
into 5 MHz (user #1), 2.5 MHz (user #2) and 2.5 MHz (user #3) in
this order in cell #1. On the other hand, the system band of 10 MHz
is divided into 5 MHz (user #1) and 5 MHz (user #2) in this order
in cell #1.
[0061] Since the pilot transmission frequency bands are fully
matched between the user #1 of cell #1 and the user #1 of cell #2,
the cross-correlation of the pilot sequence between the user #1 of
cell #1 and the user #1 of cell #2 is suppressed, if the CAZAC
sequence having the same prime number length is allocated to the
pilot signal for each user.
[0062] However, since the pilot transmission frequency bands are
not fully matched between the user #2 of cell #1 and the user #2 of
cell #2, or between the user #3 of cell #1 and the user #2 of cell
#2, the cross-correlation value can not be suppressed, even if the
CAZAC sequence is allocated to the pilot signal. That is, the
interference between cells is increased, resulting in poor
characteristic.
[0063] FIG. 9 is a view showing an example in which the division
patterns of pilot transmission frequency band are matched between
cells. Referring to FIG. 9, the system band of 10 MHz is divided
into 5 MHz (user #1), 2.5 MHz (user #2) and 2.5 MHz (user #3) in
this order in both cell #1 and cell #2. Therefore, since the pilot
transmission frequency bands are fully matched between cell #1 and
cell #2, the cross-correlation of the pilot sequence between cell
#1 and cell #2 is suppressed, if the CAZAC sequence having the
prime number length is allocated to the pilot signal for each
user.
[0064] Thus, division pattern server 10 gives the same pilot
transmission frequency division pattern to base stations 11, 12 in
the predetermined range to make the sequence lengths (frequency
bandwidth) of the pilot pattern and the frequency bands for base
stations 11, 12 in that range consistent.
[0065] By giving the same pilot transmission frequency division
pattern to base stations 11, 12 in the predetermined range, the
cross-correlation value of pilot sequence between cells can be
reduced in the predetermined range.
[0066] In the following, one method of deciding the predetermined
range of base stations 11, 12 to be given the same division pattern
will be described.
[0067] As described above, there are various factors for deciding
the appropriate division pattern, including, for example, a
tendency of the band requested by the mobile station within each
cell, a scheduling algorithm for giving a transmission permission
to the mobile station, a difference in the received signal quality
due to distance from the base station, and interference between
cells with the cross-correlation characteristic. Among others, the
scheduling algorithm is supposedly common within the 3GPP-LTE
system of this embodiment.
[0068] The tendency of the band requested by the mobile station
within each cell and the difference in the received signal quality
due to distance from the base station may belong to the properties
of the cell caused by the communication use form of the user or the
topography. Therefore, the cells having similar properties are
supposedly placed in similar situation of these factors. For
example, it is supposed that a plurality of cells adjacent to each
other in the urban area have similar tendency of the band requested
by the mobile station, and similar tendency of the difference in
the received signal quality due to distance from the base station.
Also, it is supposed that the cells adjacent to each other in the
suburbs have similar tendency.
[0069] From the above description, in this embodiment, base
stations 11, 12 constructing the adjacent cells having similar
properties are defined as the predetermined range (group of base
stations for matching division patterns).
[0070] In this embodiment, a plurality of selectable division
patterns are determined beforehand, and stored in base stations 11,
12 and division pattern server 10. FIG. 10 is a view showing one
example of predetermined division patterns in the first embodiment.
Referring to FIG. 10, three division patterns, division patterns #1
to #3, are prepared in this embodiment.
[0071] Base station 11, 12 selects the division pattern suitable
for the self cell from them, and notifies it as a desired division
pattern notification to division pattern server 10. Division
pattern server 10 decides the division pattern suitable for the
group of base stations, based on the desired division pattern
notifications from plural base stations 11, 12 belonging to the
group of base stations for making the division patterns consistent.
And division pattern server 10 dictates the decided division
pattern to all base stations 11, 12 belonging to the group of base
stations.
[0072] For example, if the division pattern #1 is notified, each of
base stations 11, 12 divides the system band of 10 MHz into halves
such as pattern #1. And base station 11, 12 allocates the band #1
and band #2 within one sub-frame of 0.5 msec to different mobile
stations making a band allocation request. The mobile station
allocated the pilot transmission frequency band transmits the pilot
signal (or pilot signal and data signal) in its band.
[0073] As described above, with this embodiment, division pattern
server 10 dictates the same division pattern to base stations 11,
12 belonging to the predetermined range, and each of base stations
11, 12 divides the pilot transmission frequency band according to
the dictated division pattern, whereby the system band can be
divided according to the appropriate division pattern to reduce
interference of the pilot signal between cells.
[0074] Also, with this embodiment, the same division pattern is
applied to the cells within the predetermined range, and therefore
the same division pattern can be applied to the adjacent cells
having similar properties, so that there is low possibility that
the division pattern unsuitable for the properties of each cell is
applied by making the division patterns identical, and there is
less harmful influence.
[0075] Also, with this embodiment, the division pattern applied
commonly to the cells in the predetermined range can be
appropriately selected, based on the desired division pattern
notified from plural base stations 11, 12 in the predetermined
range, whereby it is possible to reduce the interference between
cells and provide the communication environment favorable for the
mobile station accommodated in each cell.
[0076] Also, with this embodiment, plural division pattern
candidates are decided beforehand, and the division pattern
selected from them is applied commonly to plural base stations,
whereby the division pattern applied to plural base stations can be
easily decided.
[0077] In the 3GPP-LTE system, the scheduling algorithm for use in
allocating the band of transmitting the data signal to the mobile
station may be supposedly a general round robin, a PF (proportional
fairness) method, or a Max C/I method. The invention is not
necessarily limited to these scheduling algorithms.
[0078] Also, in this embodiment, one division pattern is selected
from three division patterns as shown in FIG. 10, but the invention
is not limited thereto. The division patterns to be prepared may
not be three, and may be other than those shown in FIG. 10.
[0079] Also, if the division pattern once decided is not changed,
it is unnecessary to prepare plural division patterns, and comprise
division pattern server 10 in the system. For example, the same
division pattern is stored beforehand in each of base stations 11,
12 in the predetermined range, and at the time of start-up, each
base station may start the operation by applying the stored
division pattern.
[0080] Also, with this embodiment, the division patterns given to
base stations 11, 12 in the predetermined range are completely
identical, but may not be completely identical. If the division
patterns identical in a part of the system band are given, the
interference between cells is reduced in the band where the same
division patterns are given.
[0081] By the way, in the scheduling for deciding the mobile
station to permit the transmission of up-stream data in the 3GPP,
it is examined to periodically measure the CQI (Channel Quality
Information) of up-link for plural mobile stations to implement the
scheduling depending on the channel situation (channel-dependent
scheduling) in both frequency and time domains. Also, it is
examined to multiplex the control channels for plural terminals
into one sub-frame.
[0082] Since the pilot signal is employed for the measurement of
CQI, it is required to multiplex the pilot signals for plural
mobile stations into the sub-frame to measure the CQI. The
multiplexing methods have been proposed, such as an FDM pilot
multiplexing method for implementing the orthogonality of the users
in the frequency domain, a CDM pilot multiplexing method for
implementing the orthogonality of the users in the code domain, and
a Hybrid method that is a combination of the above two methods.
[0083] The FDM pilot multiplexing method involves dividing the band
into plural comb teeth and allocating a different comb tooth to
each user, and was proposed in "3GPP R1-060878, "EUTRA SC-FDMA
Uplink Pilot/Reference Signal Design & TP", Motorola". Thereby,
the orthogonality between users is implemented in the frequency
domain.
[0084] The CDM pilot multiplexing method involves allocating the
mutually orthogonal codes to the users, and was proposed in "3GPP
R1-060925, "Comparison of Proposed Uplink Pilot Structures for
SC-FDMA", Texas Instruments". Thereby, the orthogonality between
users is implemented in the code domain.
[0085] In this literature, there was proposed a method for
generating plural orthogonal codes from one CAZAC sequence by
repeatedly making a cyclic shift (Q sample) having the length of
the maximum delay time or more of the assumed channel to the CAZAC
sequence to produce plural sequence.
[0086] FIG. 11 is a view showing the generation of orthogonal codes
for use in the CDM pilot multiplexing method. Referring to FIG. 11,
the user #0 is allocated the CAZAC sequence with a cyclic shift
amount of 0, the user #1 is allocated the CAZAC sequence with a
cyclic shift amount of Q, and the user #2 is allocated the CAZAC
sequence with a cyclic shift amount of 2Q.
[0087] With this method, the cyclic shift amount Q is set to the
maximum delay time or more of the assumed propagation path, whereby
the orthogonality of pilot signals for the users is also assured in
the multi-path environment. The number of codes obtained from one
CAZAC sequence by this method is roughly given by (pilot sequence
length/cyclic shift amount). In an example of FIG. 11, M codes are
obtained. And plural codes orthogonal to each other, which are
generated in this manner, are allocated to the users to implement
the orthogonality between users.
[0088] Also, in this literature, the number of users multiplexed
can be further doubled by code multiplexing of SB#1 and SB#2 with
an SF (Spreading Factor) of 2. That is, if the number of users
multiplexed is U, U users are divided into former half U/2 users
and latter half U/2 users, whereby the number of orthogonal users
can be doubled by multiplying SB#1, SB#2 by {+1, +1} code for the
former half U/2 users, and SB#1, SB#2 by {+1, -1} code for the
latter half U/2 users.
[0089] The Hybrid method is a combination of the FDM pilot
multiplexing method and the CDM pilot multiplexing method, and was
proposed in "3GPP R1-061193, "Multiplexing Method for Orthogonal
Reference Signal for E-UTRA Uplink", NTT DoCoMo".
[0090] In the Hybrid method, the users having different pilot
transmission bandwidths are multiplexed by the FDM pilot
multiplexing method, and the users having the same pilot
transmission bandwidth are multiplexed by the CDM pilot
multiplexing method. In this manner, the users having different
pilot transmission bandwidths are multiplexed by properly using the
FDM and the CDM, while the number of codes that can be secured at
the same time can be increased over the FDM pilot multiplexing
method.
Second Embodiment
[0091] In a second embodiment, one example of the FDM pilot
multiplexing is shown. The system configuration and the frame
format in the second embodiment are the same as shown in the first
embodiment.
[0092] FIG. 12 is a view showing one example of predetermined
division patterns in the second embodiment. In the second
embodiment, it is assumed that two division patterns are determined
beforehand in one example as shown in FIG. 12.
[0093] In division pattern #1, the system band of 10 MHz is equally
divided into two bands #1 and #2 of 5 MHz. Further, each of bands
#1 and #2 is divided into four groups like comb teeth. This is
denoted as RPF (Repetition Factor)=4.
[0094] In division pattern #2, the system band of 10 MHz is divided
into three bands #1, #2 and #3. Band #1 is 5 MHz and bands #2 and
#3 are 2.5 MHz. Further, each of bands #1, #2 and #3 is divided
into four groups like comb teeth with RPF=4, like pattern #1.
[0095] At the time of starting the operation of the base station,
division pattern server 10 selects any one division pattern from
division patterns #1, #2, and notifies the index of selected
division pattern to all base stations 11, 12 belonging to the group
of base stations to which the same division pattern is applied.
[0096] Each of notified base stations 11, 12 allocates the
frequency to each mobile station (user), using the notified
division pattern. For example, when division pattern #1 is
selected, each of base stations 11, 12 divides the system band of
10 MHz into halves like division pattern #1, and further divides
each band #1, #2 into four groups like comb teeth. And each of base
stations 11, 12 allocates comb teeth 1 to 4 belonging to band #1
and comb teeth 5 to 8 belonging to band #2 within division pattern
#1 to different mobile stations (users) making the band allocation
request for every sub-frame. That is, the pilot transmission band
is allocated to up to eight users for every sub-frame.
[0097] Herein, since comb teeth 1, 2, 3 and 4 are allocated to
different mobile stations in band #1 of division pattern #1, four
mobile stations can transmit the pilot signal. That is, the CQI
measurement for four mobile stations is allowed. And if data
transmission is permitted for the mobile station allocated comb
tooth 1 in the scheduling based on the results of CQI measurement,
for example, the mobile station only can transmit the data signal.
Meanwhile, the mobile stations allocated comb teeth 2, 3 and 4
transmit the pilot signal only for CQI measurement or transmit the
control signal and pilot signal only, but do not transmit the data
signal.
[0098] Similarly, the mobile station only allocated comb tooth 1
may transmit the data signal, but the mobile stations allocated
comb teeth 2, 3 and 4 may not transmit the data signal, but may
transmit the control signal. In this case, the mobile stations
allocated comb teeth 2, 3 and 4 may transmit the control signal in
LB#1 (see FIG. 1). Also, this is the same with band #2 of division
pattern #1.
[0099] In the second embodiment, like the first embodiment, it is
unnecessary that the scheduling algorithm is particularly
limited.
[0100] Also, in the second embodiment, like the first embodiment,
the division patterns may be changed during operation of the
system.
Third Embodiment
[0101] In a third embodiment, another example of the FDM pilot
multiplexing is shown. The system configuration and the frame
format in the third embodiment are the same as shown in the first
embodiment.
[0102] FIG. 13 is a view showing one example of predetermined
division pattern in the third embodiment. In the third embodiment,
it is assumed that one division pattern is determined beforehand in
one example as shown in FIG. 13. Division pattern #1 is stored in
each of base stations 11, 12.
[0103] In division pattern #1 of FIG. 13, the system band of 10 MHz
has frequency divided like comb teeth with RPF=2. And comb tooth 1
spreads over the entire band of 10 MHz. Comb teeth 2, 3 spread over
the band of 5 MHz. Comb tooth 2 spreads over band #1 of 5 MHz, and
comb tooth 3 spreads over band #2 of 5 MHz.
[0104] At the time of starting the operation, each of base stations
11, 12 allocates the frequency to each mobile station, using the
division pattern #1. For example, in a certain sub-frame, comb
tooth 1 is allocated to the mobile station making a band allocation
request. The mobile station allocated comb tooth 1 transmits the
pilot signal at the frequency of comb tooth 1 and transmits the
data signal over 10 MHz.
[0105] Also, in the sub-frame, the mobile stations allocated other
two comb teeth 2, 3 can transmit the pilot signal for CQI
measurement over 5 MHz for bands #1, #2. Thereby, the CQI
measurement for the mobile station that transmits the pilot signal
is made, and the band allocation for data transmission in the
subsequent sub-frame can be judged based on the results of CQI
measurement.
[0106] In another example, conversely, in a certain sub-frame, comb
teeth 2, 3 are allocated to different two mobile stations making
the band allocation request. The two mobile stations allocated comb
teeth 2, 3 transmit the pilot signal at the frequency of comb teeth
2, 3 and transmit the data signal over the allocated band of 5 MHz.
Further, in the sub-frame, comb tooth 1 can be allocated to another
mobile station. The mobile station allocated comb tooth 1 can
transmit the pilot signal for CQI measurement over the band of 10
MHz.
[0107] Thereby, the CQI measurement for the mobile station that
transmits the pilot signal is made, and the band allocation in the
subsequent sub-frame can be judged based on the results of the CQI
measurement.
[0108] In the third embodiment, like the first embodiment, it is
unnecessary that the scheduling algorithm is particularly
limited.
[0109] Also, in the third embodiment, like the first embodiment,
plural division patterns may be prepared and changed during
operation of the system.
Fourth Embodiment
[0110] In a fourth embodiment, one example of the CDM pilot
multiplexing is shown. The system configuration and the frame
format in the fourth embodiment are the same as shown in the first
embodiment.
[0111] FIG. 14 is a view showing one example of predetermined
division patterns in the fourth embodiment. In the fourth
embodiment, it is assumed that two division patterns are determined
beforehand in one example as shown in FIG. 14.
[0112] In division pattern #1, the system band of 10 MHz is divided
into two bands #1 and #2 of 5 MHz. Also, in division pattern #2,
the system band is divided into three bands #1, #2 and #3. Band #1
is 5 MHz, and bands #2, #3 are 2.5 MHz.
[0113] At the time of starting the operation of the base station,
division pattern server 10 selects any one division pattern from
two division patterns #1, #2, and notifies the index of selected
division pattern to all base stations 11, 12 belonging to the group
of base stations to which the same division pattern is applied.
[0114] Each of notified base stations 11, 12 allocates the
frequency to each mobile station, using the dictated division
pattern. For example, when division pattern #1 is selected, each of
base stations 11, 12 divides the system band into halves like
division pattern #1, and further allocates each band #1, #2 to four
mobile stations. The four mobile stations (users) perform the code
division multiplexing of pilot signals orthogonal in the code
domain into the same frequency. That is, the pilot transmission
band can be allocated to up to eight users for every sub-frame.
[0115] In the fourth embodiment, like the first embodiment, it is
unnecessary that the scheduling algorithm is particularly
limited.
[0116] Also, up to four mobile stations transmit the pilot signal
in band #1 of division pattern #1 in the fourth embodiment, but
only one mobile station of them transmits the data signal. That is,
other three mobile stations transmit the pilot signal only for CQI
measurement, or transmit the pilot signal and the control signal
only. Base station 11, 12 makes the CQI measurement, using the
pilot signals from four mobile stations, and makes the following
scheduling, based on the measurement results.
[0117] Similarly, only one mobile station may transmit the data
signal, and other three mobile stations may not transmit the data
signal but may transmit the control signal. In this case, other
three mobile stations may transmit the control signal in LB#1 (see
FIG. 1). Also, this is the same with band #2 of division pattern
#1.
[0118] Also, in the fourth embodiment, like the first embodiment,
the division patterns may be changed during operation of the
system.
Fifth Embodiment
[0119] In a fifth embodiment, one example of the FDM/CDM Hybrid
pilot multiplexing is shown. The system configuration and the frame
format in the fifth embodiment are the same as shown in the first
embodiment.
[0120] FIG. 15 is a view showing one example of predetermined
division patterns in the fifth embodiment. In the fifth embodiment,
it is assumed that two division patterns are determined beforehand
in one example as shown in FIG. 15.
[0121] In division pattern #1, the system band of 10 MHz is divided
into two bands #1 and #2 of 5 MHz. Further, each band #1, #2 of 5
MHz has frequency divided into two groups like the comb teeth with
RPF=2. In FIG. 15, comb tooth 1 is for the band of 10 MHz and comb
teeth 2, 3 are for the band of 5 MHz.
[0122] In division pattern #2, the system band is divided into
three bands #1, #2 and #3. Band #1 is 5 MHz, and bands #2, #3 are
2.5 MHz. Further, each band #1, #2 and #3 is divided into two
groups like the comb teeth with RPF=2, like division pattern #1. In
FIG. 15, comb tooth 1 is for the band of 10 MHz, and comb tooth 2
is for the band of 5 MHz, and comb teeth 3, 4 are for the band of
2.5 MHz.
[0123] At the time of starting the operation of the base station,
division pattern server 10 selects any one division pattern from
two division patterns #1, #2, and notifies the index of selected
division pattern to all base stations 11, 12 belonging to the group
of base stations to which the same division pattern is applied.
[0124] Each of notified base stations 11, 12 allocates the
frequency to each mobile station, using the notified division
pattern. For example, when division pattern #1 is selected, each of
base stations 11, 12 can allocate comb teeth 1, 2 and 3 to plural
mobile stations for every sub-frame. For example, comb tooth 1 is
allocated to different two mobile stations, comb tooth 2 is
allocated to different two mobile stations, and comb tooth 3 is
allocated to different two mobile stations. The mobile stations
allocated the same comb tooth perform the code division
multiplexing of pilot signals orthogonal in the code area into the
same frequency.
[0125] The mobile stations having different allocated bands perform
the FDM multiplexing, while the mobile stations allocated the same
transmission band perform the CDM multiplexing.
[0126] In the system with the division patterns as shown in FIG.
15, it is possible to suppress the interference between cells
within all the divided bands in a situation where the same division
pattern is given to the base stations in the predetermined range
and plural mobile stations use the system band by frequency
division multiplexing.
[0127] In the fifth embodiment, like the first embodiment, it is
unnecessary that the scheduling algorithm is particularly
limited.
[0128] Also, in the fifth embodiment, like the first embodiment,
plural division patterns may be prepared and changed during
operation of the system.
[0129] While preferred embodiments of the present invention have
been described using specific terms, such description is for
illustrative purposes only, and it is to be understood that changes
and variations may be made without departing from the spirit or
scope of the following claims.
* * * * *